WDM (Wavelength Division Multiplexing) is a technology that multiplexes several signals over a single optical fiber by optical carriers of different wavelength, using light from a laser or a LED. This can take greater advantage of the enormous bandwidth of optical fiber has. WDM systems are popular in fiber optic network because they allow to expand the capacity of the network without laying more fiber. Capacity of a given link can be expanded by simply upgrading the multiplexer and demultiplexer at each end. By using WDM and optical amplifiers, they can accommodate several generations of technology development in their optical infrastructure without having to overhaul the backbone network.
CWDM is short for Coarse wavelength division multiplexing while DWDM is short for Dense wavelength division multiplexing. In general, a CWDM (coarse WDM) MUX/DEMUX deals with small numbers of wavelengths, typically eight, but with large spans between wavelengths (spaced typically at around 20nm). A DWDM (dense WDM) MUX/DEMUX deals with narrower wavelength spans (as small as 0.8nm, 0.4nm or even 0.2nm), and can accommodate 40, 80, or even 160 wavelengths.
Metropolitan networks or MAN (Metropolitan Area Network) are networks that cover areas of a city or nearby cities that interface between access networks and backbone transport over long distances. The needs of these networks are typically scalability, low cost, flexibility, robustness, transparency and bandwidth relatively high and tailored to the client. The demand for transport capacity in the metropolitan area is growing due to the introduction of services and applications with high consumption of bandwidth. This need for bandwidth in the metropolitan network a few years ago raised a great interest in WDM (Wavelength Division Multiplexing), as well as the transparency inherent in this technology is well suited to this environment, characterized by the need to integrate a wide range of clients, services and protocols. However, these systems did not meet expectations at any time, mainly because they had a very high cost and did not allow a rapid return on investment in their acquisition and deployment. However, the maturity of the technology have been realized WDM systems tailored specifically to the metropolitan area, offering high bandwidth at relatively low cost. Within the family of WDM technology, the most economically competitive over short distances is the CWDM (Coarse WDM). CWDM technology benefits from lower cost of optical components associated with a lower-tech, although limited in capacity and distance, is well suited to the needs of enterprise networks and metropolitan short distance.